In recent years, in transmission devices such as layer 2 switches used in Ethernet (registered trademark), link aggregation in which a plurality of physical lines are treated virtually as a single line is used in order to expand communication bands and achieve redundancy of physical lines. In Ethernet (registered trademark), an operation, administration, and maintenance (OAM) function (hereafter referred to as a maintenance administration function) is used, in which faults of layer 2 switches belonging to a network and faults between layer 2 switches are monitored by transmitting and receiving OAM frames (hereafter referred to as maintenance administration frames), which are frames for operation, maintenance, and administration purposes.
As a related technology, a communication device such as a layer 2 network device has a first port that transmits and receives data frames with a first communication device, and has a plurality of second ports that transmit and receive data frames with a second communication device by link aggregation. The communication device has a way of duplicating OAM frames, with which an OAM frame received from the first port is duplicated so as to be transmitted to all of the plurality of second ports. A technology is known with which link faults between communication devices are detected by a communication device that transfers OAM frames to all links forming a link aggregation (see Japanese Laid-open Patent Publication No. 2008-131615).
In the transmission device 50 that forms a physical port 55 depicted in FIG. 16, since maintenance administration frames are transferred from a line card 52 to a line card 53 even if a port fault occurs, faults within the transmission device 50 are able to be monitored using a maintenance administration function.
A transmission device 70 that is used in the aforementioned maintenance administration technology and is depicted in FIG. 17 forms a link aggregation group (LAG) in which a plurality of ports are bundled together by link aggregation. If all of the ports belonging to LAG 77 are in a fault state (link-down state), an assignment unit 721 stops the transfer of frames from a line card 72 to line cards 73 to 75. Link aggregation is hereafter also referred to as LA.
The stopping of the transfer of frames by the assignment unit 721 is likewise applied also to user frames for carrying out requests and data transfer and so on, and to maintenance administration frames that confirm network communication. User frames and maintenance administration frames are hereafter also jointly referred to as frames.
In the case of a port fault such as the poor connection or disconnection of a cable, a card fault due to the failure of a card inside a device, and an inter-card fault such as the severing of a signal line between cards (hereafter also referred to as a fault other than a port fault, and also as a device internal fault), maintenance administration frames are likewise not communicated within the transmission device 70. Consequently, there has been a problem in that an administrator is not able to specify a port fault and a fault other than a port fault even when using a maintenance administration function implemented by a network operation system (hereafter referred to as OpS).